This has been an eventful week for those of us who study the dynamics of recent selection in humans. The most significant event was the publication of a paper describing genetic analysis of a long selection experiment in Drosophila. Although the experiment differs from most natural instances of selection in some important ways, the results give some very helpful corroboration that the recent human pattern of adaptive evolution was rapid and of an expected pattern for massive selection on many traits.
Meanwhile, Jonathan Pritchard and Anna Di Rienzo have a short review in the current Nature Reviews Genetics [1], discussing the idea that a large fraction of adaptive evolution may be difficult to find with current genetic evidence.
Their idea is that polygenic adaptations are unlikely to occur by successive "sweeps" of new adaptive mutations.
It seems likely to us that, as in traditional quantitative genetic models, many — possibly even most — adaptive events in natural populations occur by polygenic adaptation. Polygenic adaptation could allow rapid adaptive shifts, yet would often go undetected using conventional methods for detecting selection. Moreover, polygenic adaptation is qualitatively different from the models of adaptive substitutions that dominate the population genetics literature.
This is not a new idea, but Pritchard and Di Rienzo review it in a productive way, and the topic is worth some deeper thought...